In a story on CycleWorld.com, Kevin Cameron goes into some of the notable failures in motorcycle development, specifically in the handling department, and in the process gives a pretty damned good explain of various fork and swingarm attempts and the reasoning behind them. Here are a few examples.
The Constant Wheelbase idea:
There was a period in English motorcycling when experts announced that best handling could only result from designs having constant wheelbase. Based on this, the telescopic fork was rejected because it lets the front wheel move back as it compresses, shortening the wheelbase. The best suspension, therefore, was a leading or trailing link fork, with its travel restricted so its motion was mostly vertical.
…shot down by nothing less than Reality:
Now reality intervened in the form of the 1950 Manx Norton, with a telescopic fork up front and a swingarm at the rear.
The Chain Swingarm Pivot Thing:
Wise men now came up with one that has been rediscovered by inventors about 50 times since then, namely, to achieve perfectly constant rear chain center distance by pivoting the swingarm on the same axis as the gearbox sprocket. This looks really attractive on paper, but when you build a powerful motorcycle this way, it squats down under power in corners and pushes the front, running wide. Hmm, closer study reveals that successful designs locate the swingarm pivot higher than this, using chain tension to generate a lift force that neutralizes acceleration squat, stopping front-end push.
Seriously? That’s truly a shocker to me… but fair enough, and this is pretty important when you’re trying to place the motor in the frame.
Finally, the Low Center of Gravity thing:
The next doctrine was that the soul of good handling is a low center of gravity…. Then it turns out that when a motorcycle rolls over for a turn, it doesn’t roll around a line through its tire footprints. It rolls around its own center–of-mass, which is about 20 to 22 inches above ground level. That in turn means that for quickest direction-changing, large masses such as engine and fuel should be close to that height.
So, conclusions? Well, we circle back around to, maybe Honda, Yamaha and others actually do have some vague idea of what they’re doing and a modern bike is a pretty damned good evolution of the art, maybe generations of engineers and riders have tried just about everything, and actually are able to design something better than I can in my quasi-engineering-inspired ramblings while driving long distances on empty turnpikes, and, yes, when trying to figure a layout for batteries and a motor in a frame, maybe, just maybe it’s a good idea to try to lay stuff out with the same C/G and sprocket location as the original beast.
There’s also an interesting discussion of turbocharging, and the problems – handling problems, mind you – with the application of power to the rear wheel that a turbo creates. Now that’s interesting. If you were to make a chart of power delivery, and put a turbo on one end, I’d guess the next stop would be a two-stroke, then a four-stroke, with an electric drivetrain at the other end. Put that in the context of handling, and, am I drawing too much of a fine line by again stating that an electric drivetrain is a completely different animal than a gas bike at speed?
I’m sure that won’t hinder the next generation of design students building all sorts of alternative structures to hang the front and rear wheels off, however.